Video Forensics: Grainy to Guilty

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Video Forensics: Grainy to Guilty

The image is haunting: Two clean-cut, cool-faced terrorists stride through an airport security checkpoint just hours before hijacking the first of two airplanes that crashed into the World Trade Center.

Captured on a surveillance camera at the Portland, Maine, airport, the grainy analog image of Mohamed Atta and Abdul Aziz Al-Omari was digitized, enhanced and released to the public in hopes of jogging the collective memory for information about the infamous duo.

The snapshot is just one example of how investigators have used the latest digital technology to hunt for additional suspects and evidence related to the Sept. 11 attacks.

In addition to digitizing countless hours of security camera tapes culled from around the country, law enforcement agents are using computer tools to touch up "wanted posters" of Osama Bin Laden and other suspected terrorists (PDF) in order to show them in westernized disguise.

Scrutinizing video feeds for clues is called video forensics and it's a relatively new field. Several powerful computer programs allow investigators to convert the blurry magnetic tapes that were once routinely trashed as useless into a clear digital format that makes for compelling courtroom evidence.

Highly refined editing tools allow forensic analysts to convert fuzzy blobs into gun-wielding suspects or stabilize shaky video in order to read the license plate on a getaway car. The result is so compelling, investigators say, that many suspects quickly confess to their crimes when confronted with their digital likeness in flagrante delicto.

But the introduction of the digital technology in courtrooms is controversial. Confronted with damning computer-generated evidence, many defense teams will question the data's authenticity.

After all, digital images can be manipulated to achieve just about any effect, as evidenced by supermarket tabloids (Batboy found in West Virginia Cave!), the unblemished bodies in porn magazines like Playboy and innumerable Hollywood flicks that involve dinosaurs, monsters or other such computerized baddies.

Despite the minefields, law enforcement plugs on.

In South Florida, where authorities say 14 of the 19 hijack suspects lived, investigators are scouring ATM videotapes in an attempt to piece together the money trail that funded the terrorist attack.

Sifting through hundreds of hours of video footage is no easy task, said Eric Kumjian, a forensic analyst/robbery detective with the Miami Dade Police Department, which is working on the case.

"A lot of the tapes are degraded because people don't know how to use the equipment, the lighting's bad, the camera angles are wrong or the magnetic tape itself has deteriorated," said Kumjian, whose division processes between 300 and 400 security tapes annually.

Kumjian's team uses the Avid Xpress video editing system to digitize analog tapes, a process that involves converting the thousands of pixels found in each frame into a computer code of ones and zeros. Next they use Dtective software to do enhancements, such as reducing ambient "noise" or background movement.

Officials in neighboring Broward County are using a competing video editing system, Adobe Premiere, said Marla Carroll, a senior forensic analyst at the Broward County Sheriff's Department.

"It's a tremendous tool," said Carroll, who recently had a bank robber plead guilty after he was confronted with Photoshop images reflecting his unusual height and features. "We can do enhancements in minutes that would have taken us days before."

In Jefferson Parish, Louisiana – a bedroom community west of New Orleans – police used an Adobe plug-in called Video Analyst to nab a murder suspect.

In that case, a college student was robbed at an ATM, tied up in a truck and set on fire, said Gene Grindstaff, the chief scientist at Intergraph Government Solutions, which manufactures the editing system. The sheriff's department sent Intergraph the surveillance tape, but the sun's glare in the camera lens made it hard to see the footage.

Using the software, Grindstaff darkened the tape to reveal the murder suspect walking up behind the customer and pulling out a gun. Then he zoomed in on the suspect and was able to record several identifying characteristics, including facial scarring, an earring and the brand of shirt he was wearing – evidence that formed the basis of his arrest, Grindstaff said.

The famous shot of Atta and Aziz Al-Omari whisking through the Portland Airport security checkpoint was made using a technique that combines seven video frames into one high-resolution image. The software, VideoFOCUS was designed by Boston-based Salient Stills. Before Sept. 11, the company catered to print media but it has recently gained more law enforcement and surveillance clients, CEO Steven Hill said.

But as the technology gets better, the cries from defense attorneys grow louder.

One famous example of what some attorneys refer to as the "Adobe Defense" occurred during the wrongful death civil suit against O.J. Simpson, when Simpson's lawyers argued that photographs of the former athlete wearing Bruno Magli shoes were doctored. The expensive Italian loafers were the same kind that left bloody footprints at the murder scene of Nicole Brown and Ronald Goldman, and Simpson vehemently denied ever owning a pair of the -– in his words – "ugly-ass" shoes. The evidence was accepted after a second source produced additional photos of Simpson sporting the footwear.

But then again, the American public had already been subjected to Time's notorious Simpson cover, in which the former athlete's mug was darkened to make him look more sinister.

On a smaller scale, photos can be tweaked to make bruises and other injuries appear worse than they really are, and such changes are virtually impossible to detect without looking at the original image files.

Defense attorneys aren't the only courtroom players who balk at digital evidence, said Erik C. Berg, a forensics analyst with the Tacoma Police Department in Washington State and a leading expert in the field.

"The prosecution also sees the boogieman in the corner," said Berg, who is frequently called as an expert witness in cases involving digital evidence. "They're afraid that they'll be accused of manipulating the images."

Berg was involved in a landmark 1996 murder trial (PDF) that hinged on computer-enhanced palm prints. In that case, bloody palm prints left on a bed sheet were obscured by the fabric's weave. Berg edited out the background so the prints –- which matched the suspects hands – stood out clearly. The defense argued that the technology was unproven, and the print was the only evidence linking the suspect to the crime scene, but the jury found him guilty of murder.

When digital evidence is disputed in court, forensic analysts must produce the original image and demonstrate how it was changed. To that end, Berg designed a tracking program, More Hits, which catalogs changes and detects when even one pixel is altered in a frame.

But the judicial system is historically slow when it comes to accepting technological advances, and the admissibility of DNA and polygraph evidence is still hotly debated in many courtrooms. The path has been no smoother for digital images.

"I think in 10 years we're going to take (digital evidence) for granted," Berg said. "But in the meantime, we have to fight the battle to get it accepted."